#include "zutil.h"

local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));

#define BASE		65521U		/* largest prime smaller than 65536 */
#define NMAX		5552
/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */

#define DO1(buf,i)	{ adler += (buf)[i]; sum2 += adler; }
#define DO2(buf,i)	DO1(buf, i); DO1(buf, i + 1);
#define DO4(buf,i)	DO2(buf, i); DO2(buf, i + 2);
#define DO8(buf,i)	DO4(buf, i); DO4(buf, i + 4);
#define DO16(buf)	DO8(buf, 0); DO8(buf, 8);

/* use NO_DIVIDE if your processor does not do division in hardware -- try it both ways to see which is faster */
#ifdef NO_DIVIDE
/* note that this assumes BASE is 65521, where 65536 % 65521 == 15 (thank you to John Reiser for pointing this out) */
#define CHOP(a)		do { unsigned long tmp = a >> 16; a &= 0xffffUL; a += (tmp << 4) - tmp; } while (0)
#define MOD28(a)	do { CHOP(a); if (a >= BASE) a -= BASE; } while (0)
#define MOD(a)		do { CHOP(a); MOD28(a); } while (0)
#define MOD63(a)	\
	do { /* this assumes a is not negative */ \
		z_off64_t tmp = a >> 32; \
		a &= 0xffffffffL; \
		a += (tmp << 8) - (tmp << 5) + tmp; \
		tmp = a >> 16; \
		a &= 0xffffL; \
		a += (tmp << 4) - tmp; \
		tmp = a >> 16; \
		a &= 0xffffL; \
		a += (tmp << 4) - tmp; \
		if (a >= BASE) a -= BASE; \
	} while (0)
#else
#define MOD(a)		(a %= BASE)
#define MOD28(a)	(a %= BASE)
#define MOD63(a)	(a %= BASE)
#endif

/* ========================================================================= */
uLong ZEXPORT adler32_z(adler, buf, len)
	uLong adler;
	const Bytef *buf;
	z_size_t len;
{
	unsigned long sum2;
	unsigned n;

	/* split Adler-32 into component sums */
	sum2 = (adler >> 16) & 0xffff;
	adler &= 0xffff;

	/* in case user likes doing a byte at a time, keep it fast */
	if (len == 1) {
		adler += buf[0];
		if (adler >= BASE)
			adler -= BASE;
		sum2 += adler;
		if (sum2 >= BASE)
			sum2 -= BASE;
		return adler | (sum2 << 16);
	}

	/* initial Adler-32 value (deferred check for len == 1 speed) */
	if (buf == Z_NULL)
		return 1L;

	/* in case short lengths are provided, keep it somewhat fast */
	if (len < 16) {
		while (len--) {
			adler += *buf++;
			sum2 += adler;
		}
		if (adler >= BASE)
			adler -= BASE;
		MOD28(sum2);            /* only added so many BASE's */
		return adler | (sum2 << 16);
	}

	/* do length NMAX blocks -- requires just one modulo operation */
	while (len >= NMAX) {
		len -= NMAX;
		n = NMAX / 16;          /* NMAX is divisible by 16 */
		do {
			DO16(buf);          /* 16 sums unrolled */
			buf += 16;
		} while (--n);
		MOD(adler);
		MOD(sum2);
	}

	/* do remaining bytes (less than NMAX, still just one modulo) */
	if (len) {                  /* avoid modulos if none remaining */
		while (len >= 16) {
			len -= 16;
			DO16(buf);
			buf += 16;
		}
		while (len--) {
			adler += *buf++;
			sum2 += adler;
		}
		MOD(adler);
		MOD(sum2);
	}

	/* return recombined sums */
	return adler | (sum2 << 16);
}

/* ========================================================================= */
uLong ZEXPORT adler32(adler, buf, len)
	uLong adler;
	const Bytef *buf;
	uInt len;
{
	return adler32_z(adler, buf, len);
}

/* ========================================================================= */
local uLong adler32_combine_(adler1, adler2, len2)
	uLong adler1;
	uLong adler2;
	z_off64_t len2;
{
	unsigned long sum1;
	unsigned long sum2;
	unsigned rem;

	/* for negative len, return invalid adler32 as a clue for debugging */
	if (len2 < 0)
		return 0xffffffffUL;

	/* the derivation of this formula is left as an exercise for the reader */
	MOD63(len2);                /* assumes len2 >= 0 */
	rem = (unsigned)len2;
	sum1 = adler1 & 0xffff;
	sum2 = rem * sum1;
	MOD(sum2);
	sum1 += (adler2 & 0xffff) + BASE - 1;
	sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
	if (sum1 >= BASE)
		sum1 -= BASE;
	if (sum1 >= BASE)
		sum1 -= BASE;
	if (sum2 >= ((unsigned long)BASE << 1))
		sum2 -= ((unsigned long)BASE << 1);
	if (sum2 >= BASE)
		sum2 -= BASE;

	return sum1 | (sum2 << 16);
}

/* ========================================================================= */
uLong ZEXPORT adler32_combine(adler1, adler2, len2)
	uLong adler1;
	uLong adler2;
	z_off_t len2;
{
	return adler32_combine_(adler1, adler2, len2);
}

uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
	uLong adler1;
	uLong adler2;
	z_off64_t len2;
{
	return adler32_combine_(adler1, adler2, len2);
}
